Here's an interesting experiment for those of you with a 40D (could be others, but the 40D has a different viewfinder than previous xxD versions) and a 50mm lens (or zoom that covers 50mm). If you're using a zoom, set it to something like approximately 45-48mm.
I try and keep both eyes open so I can see if I'm going to run into something when shooting. What I noticed is somewhere in the 45-50mm range, the "view" through the viewfinder is the exact same perspective as my non-viewfinder eye. Just like it is with my 35mm film camera and a 50mm lens.
50mm is every so slightly zoomed in, but not 1.6 times zoomed in... it's a much smaller percentage.
Someone else can do the math, but the crop format along with viewfinder sizing and some viewfinder cropping yields almost the same perspective.
I just found this surprising. I know that compared to a FF view (again, using an old film camera) the image is 1.6x smaller, but I guess I was just surprised that viewfinder perspective didn't have the same factor!
Anyway, enough random rambling. Just very interesting results to me at least!